Re: [PATCH v2 1/7] Compiler Attributes: Add __alloc_size() for better bounds checking

Miguel Ojeda
2021-08-19T00:04:59Z

On Wed, Aug 18, 2021 at 11:40 PM Kees Cook <keescook@chromium.org> wrote:
>
> GCC and Clang can use the "alloc_size" attribute to better inform the
> results of __builtin_object_size() (for compile-time constant values).
> Clang can additionally use alloc_size to inform the results of
> __builtin_dynamic_object_size() (for run-time values).
>
> Because GCC sees the frequent use of struct_size() as an allocator size
> argument, and notices it can return SIZE_MAX (the overflow indication),
> it complains about these call sites may overflow (since SIZE_MAX is
> greater than the default -Walloc-size-larger-than=PTRDIFF_MAX). This
> isn't helpful since we already know a SIZE_MAX will be caught at run-time
> (this was an intentional design). Instead, just disable this check as
> it is both a false positive and redundant. (Clang does not have this
> warning option.)

Thanks!

Reviewed-by: Miguel Ojeda <ojeda@kernel.org>

Cheers,
Miguel